Various formats may be utilized for optical signal modulation in silicon photonics, including, return-to-zero (RZ) and non-return-to-zero (NRZ) on-off keying (OOK), RZ and NRZ differential phase shift keying (DPSK), quadrature phase shift keying (QPSK), and so forth. A four-level pulse amplitude modulation (PAM-4) format may also be utilized in complementary metal-oxide-semiconductor (CMOS) based integrated circuits for optical signal modulation.